The process sequence of the existing production lines is shown in FIG. 1. The saw-damage and impurities present on the raw silicon wafers are removed with a wet etching. Simultaneously with this process a defined surface texture is obtained. A phosphorous containing precursor is deposited that serves as the phosphorous source during the emitter diffusion in a horizontal passage furnace. A phosphorous glass layer is formed during diffusion. This layer is removed with wet etching prior to the deposition of a SiNx anti-reflection coating. Front- and back-side metallization is realized by screen printing and firing of metallization pastes. Finally, laser ablation electrically isolates the emitter and collector at the edge of the wafer.
The cell efficiency obtained with the process sequence described in FIG. 1 is limited by the surface condition that is obtained after the phosphorous glass removal. The non-ideal surface condition may originate from:                (a) an excessively large phosphorous concentration;        (b) residues left from the preceding processes that are not removed by the standard wet chemical glass removal;        (c) segregation of impurities from the bulk to the surface during preceding processes that are not removed by the standard wet chemical glass removal; and        (d) nanometer-scale surface roughness (e.g. porous silicon).        